Mayor Bloomberg announced yesterday that PS 90 in Brooklyn has scrapped Justin Bieber’s ballad “Baby” from being belted out at the school’s June 20 kindergarten graduation ceremony.

The move was triggered by a report in Sunday’s Post that Principal Greta Hawkins approved Bieber’s flirty teen song but pulled the plug on Lee Greenwood’s patriotic “God Bless the USA.”

Hawkins claimed Greenwood’s revered song was offensive to some cultures and religions, stunned staffers said.

But Bloomberg and Schools Chancellor Dennis Walcott said Hawkins had a change of heart and concluded that Bieber’s “Baby” was inappropriate for 5-year-olds. They insisted they not did pressure her to do so.

“The principal has decided she’s not going to sing that song. It’s the principal’s decision, and we support the principals,” Bloomberg said during a press conference at the Bushwick HS campus.

Walcott said, “Now as far as Justin Bieber, I understand some of the issues people raised. It’s my understanding that song will not be part of the ‘moving up’ ceremony as well . . . I support our principals along that line.

But “God Bless the USA” was not put back in the program — drawing a rebuke from singer Greenwood and political leaders.

“I’ve been singing my song for 30 years. I sing it everywhere — Carnegie Hall, grammar schools,” Greenwood told The Post yesterday.

“To say it’s inappropriate for a 5-year-old is absolutely ridiculous.”

Greenwood said compared to “God Bless the USA,” Bieber’s romantic ballad was “a little over their head.”

“I think [Principal Hawkins is] confused between allegiance and worship. I don’t think it’s a religious issue to salute the flag. You always respect the flag. That’s just simple for me. A religion that says you can’t do that is out of place,” he said.

“I’m just disappointed. I’ve sung it at many elementary schools myself. It’s always a wonderful moment,” he said, adding that the students get “wide eyed.”

Political and community leaders have joined the battle, demanding that “God Bless the USA” be reinserted into the PS 90 program.

Queens Councilman Peter Vallone launched a campaign on his Facebook page to do so.

“This song expressed a genuine devotion to our country. No one should be concerned about anyone who might be offended by that . . . The chancellor needs to rethink his decision and allow the kids to sing this beautiful song,” Vallone said.

Meanwhile, Hawkins faces other problems. The Department of Education is investigating a parent’s claim that she hit a fifth-grader after confiscating the boy’s cellphone.

The NYPD’s hate-crimes task force is also investigating three anonymous letters to Hawkins that contained “anti-black” content, sources said.